The measurement of size of rigid objects with screw-type micrometers, pivotal caliper devices and sliding calipers is relatively simple since the degree of contact with the object can be readily determined by the user with some experience and utilizing the touch sensation only.
For yieldable objects such as foam material, rubber or elastomeric materials, the results of such measurements are highly dependent upon the force with which the caliper members bear upon the object. In these cases and in the measurement of tissue thicknesses, especially tumor tissue size, the variations in measurement can be comparatively large because of the sensitivity of the object to compression. The calipers utilized for this purpose in the past have included sensing arms which were urged against the tissue by the hand of the surgeon or a helper. When various individuals attempt to take the measurement, a variety of results generally will be obtained.